LibreOffice can use wildcards, or regular expressions, or none - depending on the settings in the
Find & Replace dialog. These settings are hidden under the
Other Options expanding group. So you need to make sure that you select the correct setting.
As you don’t tell which search string are you using, and which text in a cell you are expecting to find, it’s hard to tell if there is anything else to take into account. Note that for formulas, there’s a setting under
Calculate, which tells if regular expressions or wildcards should be used in searches.